Time for a new battery? How will a degraded battery act under load compared to resting?

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ultimatenic   1 mW

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Time for a new battery? How will a degraded battery act under load compared to resting?

Post by ultimatenic » Oct 15 2018 2:17pm

I've been having some issues with my ebike battery. It is a 48V 15AH ping with high rated BMS (continuous discharge of 60amps). My bike is a 1500W and likely pulls 30-50AMP at full throttle. I've had the battery about 2-3 years and have always ridden full throttle, always.

The issue is that the low voltage cut off is being triggered due to voltage drop but through testing I have not been able to narrow down any low cell group. Basically I can run the bike motor at full throttle with no rider (back wheel propped up and wheel spinning freely). They second there is a rider on the bike at full throttle the battery cuts off within seconds. Plugging the battery back in for a second brings the system to life again. I've tested the battery within about 2 minutes after cut-off and all the cells read 3.4-3.5, so I cant narrow it down to one cell group over another. My theory is all the cells are degraded but just not showing so at rest.

I guess the most illuminating question for me is this: Is it possible for a degraded cell pack to read 3.5 volts per cell, and 56/58v for entire pack at rest (even after a cut-off)? Is it possible for the battery to still be able to output 20amps or 30amps but under full load(with a rider on the bike) pulling 50amps the battery just doesn't have it and it triggers the shut down? Is this behavior conducive with an aging LiFePO pack?

The other theory is that there is a fault on the BMS?

(PS I was able to test this battery on another bike and I saw the same behavior. Bike would run fine but at full throttle we saw voltage drop to below 48V triggering a shutdown. Then battery returned to nominal voltage of above 52V)

New Battery? More testing? BMS?

Any insight is greatly appreciated.
Yes I ride an E-bike to work at an electric utility and yes I am a Super Nerd

Yermommy   1 W

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Re: Time for a new battery? How will a degraded battery act under load compared to resting?

Post by Yermommy » Oct 17 2018 8:42pm

To begin: most batteries should be run at 50% of their rated discharge for longevity.

Unloaded vs loaded pulls make a HUGE difference. My battery pack sags 0.5 volts when I spin the wheel unloaded at full throttle but sags 7-10v when I sit on the bike.

2-3 years of repeated full throttle abuse will absolutely deteriorate the overall health of the batteries. No shame in doing it, but it does mean that you will need to replace the pack sooner than if it was babied.

Do you know what type of cells are in your battery? I know you said LiFePO but do you know the make and model?

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fechter   100 GW

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Re: Time for a new battery? How will a degraded battery act under load compared to resting?

Post by fechter » Oct 18 2018 9:28am

Sounds pretty typical of a pack that is getting old. Voltages look OK at rest but sag a lot under load. The internal resistance of the cells has increased to the point where you hit cutoff. 4C discharge is really a lot for those cells.

You could lower the cutoff voltage, but that would just let you accelerate the damage. Lowering the current limit on the controller would work.

As long as the cells are balanced, there's not much you can do. A bigger pack would be advised if you want to stay at 60A.
"One test is worth a thousand opinions"

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dogman dan   100 GW

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Re: Time for a new battery? How will a degraded battery act under load compared to resting?

Post by dogman dan » Oct 24 2018 9:11am

That thing did damn good to last this long, at that rate. Going easier on them, I never got much more than 3 years from a ping myself. Some got 4, a few even more. But 3 years is typical. From what you say, all your cells are the same, they sag like grannies tits.

The cells have high internal resistance now, so when you hit the throttle, they are just making heat inside now, and voltage sags like crazy. Betcha they are slightly puffed now, or worse.

A 20 ah would be good next time, if carrying that much weight is not a problem. Its too much for top of a rear rack imo, unless its a cargo bike.

Best bet would be to limit amps to 20, and get another just like it. It will seem lame, but might go 4 years then. Other things made mine last only 3, too hot all day in summer mostly. Park in really hot garage in the afternoons cost me I'm sure.


I hate to recommend lipo, or other lighter chemisty, not since my house burned. But that controller needs a much larger, or much stronger battery. Lipo is hazardous, and wears out in 2 years for sure, but if you hot rod that bike, its lipo time. A 15 ah lipo pack will only sag 2v or less under heavy load. You'll like that! When they sag like your ping did new, they are used up.

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ginekolog   100 mW

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Re: Time for a new battery? How will a degraded battery act under load compared to resting?

Post by ginekolog » Oct 24 2018 3:42pm

The same thing happend to my Panasonic NCR18650PF. I have 13S4P configuration. They should hold 40 A max burst. I used them on BBS02 with regular discharge of 15-20 A. After 2,5 years (and about 300 cycles, 8000 km with BBS02) they sagg a lot (LCV cuts out at 41V) when on discharge above 10 A. That means i still use it as secondary battery but can not use it for steep climbs. Capacity is still at around 70-80%.

My theory is that I killed them with hard discharge and perhaps with riding them on sub zero temepratures (about 20 times, they sagged a lot when they were cold). I did not expect that battery will need replacing after 2,5 years. :confused:

Any other thoughts?
Giant Trance X2 + BBSHD + 52V + 17,5 Ah = :bolt: :bigthumb: :D

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fechter   100 GW

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Re: Time for a new battery? How will a degraded battery act under load compared to resting?

Post by fechter » Oct 24 2018 11:18pm

Running a pack until cutoff is bad for cycle life too. Cell IR jumps way up when it get to a low state of charge and high discharge rates will start heating the insides in a detrimental way. If your pack is big enough so you rarely use over 50%, it will last much longer.
"One test is worth a thousand opinions"

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